
In a large mixing bowl, whisk together the oil, vinegar, mustard, honey, salt, and pepper until emulsified.
Add the red onions first and allow them to sit in the dressing for 10 minutes while preparing the remaining ingredients.
Add the kidney beans, cannellini beans, chickpeas, bell pepper, celery, parsley, and dill and toss to combine.
Serve at room temperature, or refrigerate for 30 minutes to allow the flavors to develop.